The present invention relates to polyol blends such as are used in preparation of molded parts and more particularly to the stabilization of such polyol blends and to improved thermoset molded parts made therefrom.
Reaction Injection Moldings (RIM) are urethanes basically consisting of a polyol and a polyisocyanate, usually with an extender (e.g. a glycol or a diamine), optionally with a blowing agent (e.g. air), optional reinforcing material (e.g. glass, mica, etc.), wetting agents, and the like, which materials are high pressure injected through a mixing head into a pre-heated mold with usual post-molding baking thereafter applied. RIM urethanes can range from low modulus to very high modulus material parts, foamed on the interior but with a smooth surface. RIM urethanes are capable of being made into very large one-piece parts which are very light in weight. Typical present-day uses of RIM parts include, for example, automobile parts (e.g. bumpers, air deflectors, fenders, front ends, etc.), business machine housings, ski boots, office furniture, and a wide variety of products.
When a glycol extender is utilized in conjunction with a long chain polyol, such as a long chain polyoxyalkylene polyol, it has been reported that the blend suffers from storage stability by separating into two phases. Such phase separation creates difficulties at the plant since mixing of the phase-separated blend must precede use of the blend whether such blend is utilized in RIM part formation or is utilized for other purposes. A variety of proposals aimed at rendering the mixture of long chain polyol and short chain diol compatible have appeared in the art. For example, U.S. Pat. No. 3,929,730 proposes to compatibilize the blend of a polyol and 1,4-butanediol by the addition of thiodiglycol or phenylenediethanolamine. U.S. Pat. No. 3,993,576 proposes to compatibilize mixtures of high molecular weight polyols and low molecular weight polyols by the addition of a butylene glycol or propylene glycol such as dibutylene glycol. U.S. Pat. No. 4,220,732 proposes to compatibilize the blend of polyol and glycol by utilizing as the glycol extender a combination of 1,4-butanediol and phenyldiethanolamine. U.S. Pat. No. 4,385,133 compatibilizes the polyol/glycol blend by employing as the polyol component a mixture of specific polyoxypropylene polyoxyethylene polyols of specific molecular weight and functionality. Other proposals involve the use of salts (potassium chloride or potassium acetate) or add a small amount of isocyanate for partial reaction and compatibilization of the blend. U.S. Pat. No. 4,581,470 teaches the use of nitrogen containing polyols as compatibilizing agents. U.S. Pat. No. 4,575,518 discloses the use of a wide variety of salts as compatibility agents for glycol/polyol blends. U.S. Pat. No. 4,576,731 teaches pre-reacting a portion of the isocyanate with the incompatible mixtures. Chain extenders prepared from proplyene oxide capped ethylene glycol have been shown to give one-phase mixtures (U.S. Pat. No. 4,518,521), as well as mixtures of 1,4-butanediol and phenylenediethanolamine (U.S. Pat. No. 3,929,730), or various butylene glycols (U.S. Pat. No. 3,995,576). U.S. Pat. No. 4,485,032 disclosed the use of substituted ureas as compatibilization agents. These prior art compatibilizing agents suffer from several deficiencies, primarily low extender levels allowed, high viscosity of resulting mixtures and limited applicability.
Despite such advances in the art, need for effectively stabilizing the polyol/glycol blend while improving the final urethane product still is a desire of the art.